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© Reproduced by permission of the AAS. Courtesy of M.A. Alpar, P.W. Anderson, D. Pines, and J. Shaham, 1983.

An illustration of two possible regimes of pinning for superfluid vortices in the crust of a neutron star. Left: the weak pinning expected when the size of the normal core, of a vortex in the crustal neutron superfluid vortex is comparable to that of a crustal nucleus. Right: the superweak pinning expected for a much larger vortex normal core. Theorists expect a substantial variation in pinning energies in crustal regions, since the superfluid coherence length reflects the rapid variation of the crustal superfluid energy gap. Weak pinning occurs when vortices pin to single nuclei in their path; superweak pinning when the core of a vortex is much larger than the size of a nucleus. The response of these different regions may be seen in the quite different time scales required for vortices to reestablish their positions following a glitch, so it is plausible that the 5.4 d, and 49 d recovery times seen in the Vela pulsar reflect the presence of significant weak and superweak pinning regions there. (Unit: 8)